With the one-syllable surname Rolf, I would eliminate the shorter names and those with pronounced w's and r's (Wren, Sage, Sora, Rowan). I like Evalina but it's not the same style and seems overly frilly next to Kolten and Keaton. Tierney is certainly of the same surname style and flows well with your last name. The drawback is that some people may hear the word "tyranny". Emlyn and Auden would just continue the same "n" ending pattern so they may not be the best options. Agnes is too clunky with your boys. I think my favourite is Mabel. Yes, it's vintage and feminine but it's also strong and solid for a "bel" name. Here are some other suggestions.